Modulation of Ovarian Physiology Elicited by Immune System Response to Pre-Breeding Vaccination in Beef Cattle

Abstract

The relationship between the immune and reproductive systems can influence reproductive success in beef cattle. Although the use of pre-breeding vaccination is invaluable for preventing against disease induced loss, negative reproductive consequences are reported after vaccination. The goals of this dissertation project was to evaluate the effects of modified-live virus (MLV) or inactivated virus vaccination (IVV) on reproductive tissue infection, corpus luteum (CL) function, and progesterone production, and to characterize the bovine immune response after vaccination and MLV re-exposure. In Experiment I (Chapter II), previously vaccinated females (n=50) were administered one of three types of vaccination and reproductive tract tissues collected for virus isolation. It was discovered all collected reproductive tissues were negative for vaccine virus. In Experiment II (Chapter III), estrous synchronized cows (n=86) were administered MLV or IVV and CL collected 10 to 13 days after vaccination. Blood samples were collected every other day from treatment administration (d0) to d 22. Cows administered MLV around estrus had decreases in both luteal cell populations and plasma progesterone concentrations. In contrast, these cows had increased concentrations of pro-inflammatory cytokines and an increase in the degree of apoptosis in the CL that formed after an abnormal estrous cycle. Collectively, these results suggested a potential shift in the immune response after vaccination, which may be responsible for the observed effects on the bovine CL. Research in Experiment III (Chapter IV) included the characterization of leukocyte populations, antibody and cytokine production that occurs after vaccination, and in Experiment IV (Chapter V), following MLV re-exposure. Cows (n=30) were synchronized and either vaccinated (IVV or MLV) or administered saline (d0). Blood samples were collected until d79 for isolation of leukocytes and quantification of antibody and cytokine concentrations. Several leukocytes were found to be affected by vaccination and over time. The changes in leukocyte population and activity, as measured by cytokine and antibody production are indicative that a pro-inflammatory environment is induced after pre-breeding vaccination. This pro-inflammatory environment is thought to contribute to the negative effects on ovarian, and especially CL function, and thus causing reproductive inefficiency after females are vaccinated close to the breeding season.